The epoxy resin adhesive has most widely been used to bond metals with each other. However, bonding with satisfactory strength cannot always be accomplished by the epoxy resin adhesive because a lowering of bonding strength may be caused by, for example, the shrinkage of epoxy resin adhesive at the time of curing reaction. In particular, when the epoxy resin adhesive is of one component adhesive type, and a trigger such as heat is employed at the time of curing reaction, the bonding strength tends to decrease because internal stress is centralized at the bonding portion due to the difference in thermal expansion coefficient from those of metals as adherends.
Moreover, the epoxy resin adhesive is generally liquid, so that the bonding step is likely to become burdensome. That is, it is difficult to apply an appropriate amount of adhesive to an adherend surface, and problems such as liquid runs are encountered.
In order to resolve these problems of the liquid adhesive, various sheeted adhesives have been developed and put on the market. However, the conventional sheeted adhesives have drawbacks in that their storage stability is poor and, when bonding and curing are conducted after long-term storage, satisfactory bonding strength (peeling strength) cannot be obtained.
The present invention has been made taking the above prior art into account. Accordingly, the present invention provides an adhesive composition which is excellent in storage stability and can bond metals, etc. with large bonding strength and whose sheeting enables simplifying bonding steps, and provides an adhesive sheet comprising the composition.